Question

In sets $a-d$, only one of the set is incorrect regarding basic strength. Select it:

• A.
• B.
• C.
• D.

Answer 1

The correct option is D

In set (a), the lone pair on (iii) is readily available for donation, so it is more basic. In (ii) the lone pair of electron is delocalised in one phenyl ring but in (i) it is delocalised in two phenyl ring so it is least available. Hence it is less basic and the given order is correct.

In set (b), lone pair is involved in resonance in (i) hence it is least basic and the lone pair of electron in (iii) is not involved in resonance hence it is readily available so it is most basic. Hence the given order is correct.

In set (d), the +H effect of $C{H}_3$ in (iii) will increase electron density on N so it is most basic. -I effect and -R effect of $N{O}_2$ in (i) will decrease the electron density in ring so it least basic. Hence the given order is correct.

In set (c), (i) has to be least basic because its lone pair of electrons are involved in resonance. In (ii) the lone pair of electrons are readily available so it is more basic than (i). In (iii) the conjugate acid formed is stabilised by two equivalent resonating structures hence it is most basic. So it follows the order,